This invention relates to a method and a circuitry for regulating the position of at least the drive of a transverse sealing device forming part of a packing machine. The circuitry includes a first motor for driving a supply conveyor advancing the articles to be packaged, a second motor for supplying the wrapper material and a third motor for driving a sealing device which provides sealing seams oriented transversely to the advancing direction of the articles.
The basic principle of a control of the above-outlined type is known. Thus, according to U.S. Pat. No. 4,549,386 a list of data is made available by means of a microprocessor in order to synchronize the motion of the transverse sealing shoes with the drive of the article conveyor and the drive for advancing the wrapper material. This prior art system makes the initial assumption that if N number of articles are packaged per minute, then a total of 1/N minute is available for all the packaging steps Thus during such a period
the article conveyor has to be moved by a distance which equals the length of one article plus the distance between two consecutive articles;
the sealing shoes have to execute a full revolution; and
the wrapper material has to be fed through one whole length for packing one article.
The above-listed three courses of motion have to occur in synchronism. In order to ensure that the sealing operation is effected synchronously with the supply of the wrapper material, the motor for driving the sealing shoes has to be controlled as a function of the feed of the wrapper material. The data group supplied by the microprocessor has a first phase with constant velocity and subsequently has a second phase with increasing velocity and an adjoining phase with decreasing velocity and a concluding fourth phase with constant velocity. The sealing shoes rotate during one phase with constant velocity over the moving wrapper web. The microprocessor determines such constant velocity and adds thereto an associated peak velocity to ensure that the sealing shoes are capable of performing a full revolution. The course of motion of the sealing shoes, however, is not slippage free between the sealing shoes and the wrapper material during the engagement phase. During the sealing phase there occurs, due to the less than optimally tuned motion of the sealing shoes a tension stress of the wrapper material or an undesired crowding (gathering) thereof.